The invention relates to forming relatively thick-walled bodies from synthetic micas. A thick-walled body is not restricted as to configuration, but, characteristically, has a wall thickness greater than about ten mils. This differentiates between articles such as wall board, electronic substrates and catalyst carriers on one hand, and paper and film products on the other.
U.S. Pat. No. 4,239,519 (Beall et al.) is directed to the preparation of inorganic gels from which ceramic papers, fibers, films, boards, and coatings can be made. The basic method for preparing those gels contemplates three general steps: (1) a fully or predominantly crystalline body is formed containing crystals consisting essentially of a lithium and/or sodium water-swelling mica selected from the group of fluorhectorite, hydroxyl hectorite, boron fluorphlogopite, hydroxyl boron phlogopite, and solid solutions among those and between those and other structurally compatible species selected from the group of talc, fluortalc, polylithionite, fluorpolylithionite, phlogopite, and fluorphlogopite; (2) that body is contacted with a polar liquid, desirably water, to cause swelling and disintegration of the body accompanied with the formation of a gel; and (3) the solid:liquid ratio of the gel is adjusted to a desired level depending upon the application therefor.
Papers, fibers, films, boards, and coatings are prepared from the gel. To impart good chemical durability thereto, these products are subsequently contacted with a source of large cations, commonly K.sup.+, Rb.sup.+, Cs.sup.+, NH.sub.4.sup.+, H.sub.3 O.sup.+, Ca.sup.+2, Sr.sup.+2, Ba.sup.+2, Ag.sup.+, Cu.sup.+, Mg.sup.+2, Pb.sup.+2, or organic polycations. This causes an ion exchange to take place between the large cations and the Li.sup.+ and/or Na.sup.+ ions from the interlayer of the crystals. Thereafter the ion-exchanged products are dried. Glass-ceramic bodies are statedly the preferred crystalline starting materials for gel formation.
The patent discloses laying up, stacking, or otherwise depositing several films or sheets one upon the other and thereafter drying the resulting composite, optionally with pressing, to form board. The patent also observes that wet gel, after flocculation via the above-described ion exchange reaction, can be pressed and dried into board or other configuration. Further experience with these techniques demonstrated that the first approach required much handling of the material, and that the resultant board frequently suffered delamination along the planes between the stacked layers. The second technique provided board of less laminar character, but the strength thereof rapidly decreased in atmospheres of relatively high humidity.